And I'm Robert Siegel. We're going to start this hour by looking at some of the tools the Obama administration is using to combat the growing terrorism threat in Syria and Iraq. In a moment, we'll ask whether financial weapons can cut the flow of money to the extremist group that's grabbing cities and towns in Iraq. But first, the Attorney General today advised European diplomats meeting Oslo, Norway that they need to do more to stop their citizens from traveling to the Middle East to fight. Eric Holder says the U.S. and its allies cannot afford to be passive. NPR's Carrie Johnson has more.

CARRIE JOHNSON, BYLINE: The Attorney General says Syria is a cradle of violent extremism, and the 7,000 foreigners who have joined the fight there represent a grave threat.

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ERIC HOLDER: The problem of fighters in Syria returning to any of our countries is a problem for all of our countries. This is a global crisis in need of a global solution.

JOHNSON: Eric Holder says his European counterparts need to seize the moment and prevent their citizens from traveling to Syria in the first place.

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HOLDER: If we wait for our nation's citizens to travel to Syria or to Iraq to become radicalized and to return home, it may be too late to adequately protect our national security.

JOHNSON: Holder urged other nations to conduct undercover operations to monitor travelers and to arrest people using laws that prohibit training and preparing for terrorism. The U.S. does that. And in recent years, Holder says Norway and France have passed similar legislation.

Former British diplomat and intelligence officer, Richard Barrett, says he mostly agrees with the Attorney General. But Barrett, now a senior vice president at the Soufan Group, says criminalizing the problem isn't enough.

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RICHARD BARRETT: Another issue is why are these people going? What is it that they're seeking there that they can't find in their own communities? And I think that's a much deeper and bigger question that is probably well worth examining.

JOHNSON: Not all the people who join the fight are likely to become terrorists, Barrett says. But he says the connections they make there are powerful.

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BARRETT: By mixing with very radical people from other countries, they may not only be influenced in their way of thinking, but also set themselves up for being part of a network in the future. If they're tapped on their shoulder by somebody they fought shoulder to shoulder with, I think they're going to feel some strong sense of loyalty, perhaps, to those people.